That is an female inverted flare fitting used for gas and brake lines. I just went thru the same issue not finding them at any local parts store and I visited them all. I ended up ordering it from MSC. They had exactly what I needed, it was cheaper that any of the normal venders. I ordered 4 fittings and the total order including shipping was just over 18 dollars. The best part was it came in two days!
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